1. Field of the Invention
The invention generally relates to sol-gel processes and formulations for fabricating .beta.-aluminum titanate (Al.sub.2 TiO.sub.5) coatings on different dense and porous substrates.
2. Description of the Prior Art
Frequently, ceramic materials with desired high temperature mechanical properties need surface modifications to improve corrosion and/or oxidation resistance. SiC and Si.sub.3 N.sub.4 are widely used high temperature structural materials for high efficiency heat engines, particulate filters, and gas turbines. The performance of SiC and Si.sub.3 N.sub.4 greatly relies on the integrity of the surface oxide layer which retards further oxidation of the underlying material. Severe strength degradation has been frequently observed when the surface protective film deteriorates as a result of chemical attack. Large pits formed after exposure in hostile environments, through either active or passive oxidation, are responsible for strength reductions. Atmospheres containing oxygen, hydrogen-steam, or alkalies are known to attack both SiC and Si.sub.3 N.sub.4.
.beta.-Al.sub.2 TiO.sub.5 is an engineering material component which is characterized by its low thermal expansion, excellent thermal shock resistance, and thermal conductivity. .beta.-Al.sub.2 TiO.sub.5 has been used in heat engines including portliners of piston heads, turbocharger linings, and insulation valves.